Bone Cancer

Ewing’s Sarcoma: Standardand Experimental TreatmentOptionsVivek Subbiah, MDPete Anderson, MD, PhDAlexander J. Lazar, MDEmily BurdettKevin Raymond, MDJoseph A. Ludwig, MD*

Address*Department of Sarcoma Medical Oncology, Division of Cancer Medicine,

Laboratory of Sarcoma Molecular Therapeutics, M.D. Anderson Cancer

Center, Houston, TX, USA.

E-mail: jaludwig@mdanderson.org

ª Springer Science+Business Media, LLC 2009

Opinion statementEwing sarcoma family tumors (EWS), which include classic Ewing’s sarcoma inaddition to primitive neuroectodermal tumor and Askin tumor, are the second mostcommon variety of primary bone cancer to afflict adolescents and young adults.Multi-disciplinary care incorporating advances in diagnosis, surgery, chemotherapy,and radiation has substantially improved the survival rate of patients with localizedEwing sarcoma to nearly 70%. Unfortunately, those advances have not significantlychanged the long-term outcome for those with metastatic or recurrent disease;5-year survival remains less than 25%. This apparent therapeutic plateau existsdespite extensive effort during the last four decades to optimize the efficacy ofcytotoxic chemotherapy through combination of chemotherapies of mechanisticallydiverse action, dose-dense scheduling (provided as frequently as every 2 weeks),increased adjuvant treatment duration, and higher dosage per cycle (facilitated withparallel strides in supportive care incorporating growth factors). As has alreadyoccurred for malignancies such as breast or colon cancer, the ‘‘-omics-based’’ revo-lution has enhanced our understanding of the molecular changes responsible forEwing’s tumor formation and identified a number of potential targets (such as IGF-1Ror mTOR) amenable to biological therapy. It has also created both a challengeand an opportunity to develop predictive biomarkers capable of selecting patientsmost likely to benefit from targeted therapy. In this review, we discuss currentstandard-of-care for patients with Ewing’s sarcoma and highlight the most promisingexperimental therapies in early-phase clinical trials.

Current Treatment Options in Oncology (2009) 10:126–140

DOI 10.1007/s11864-009-0104-6

IntroductionThe second most common bone cancer in adolescentsand young adults after osteosarcoma, Ewing sarcomafamily tumors (EWS) affect between 300 and 560people in the United States each year [1]. Thisincludes patients diagnosed with extraskeletal Ewingsarcoma, small cell tumor of the thoracopulmonaryregion (Askin tumor), and soft-tissue-based primitiveneuroectodermal tumors (PNET). These Ewing’s fam-ily tumors harbor identical cytogenetic changesresulting in primitive mesenchymal stem cells capableof multilineage differentiation along an osteogenic,adipogenic, or neurogenic spectrum [2–6]. Althoughthe prognosis is markedly better for those withoutradiographic evidence for disseminated disease, thevast majority will develop rapid recurrence, often tothe lung, unless systemic chemotherapy is provided.Therefore, all patients require coordinated multimo-dality treatment that combines systemic chemother-apy (neoadjuvant and adjuvant) with local controlmeasures such as surgery and/or radiation, preferablyat institutions with expertise caring for patients diag-nosed with EWS. Though large tumor size (or vol-ume), axial/pelvic location, poor chemotherapyresponse, and older age at diagnosis are known toadversely affect survival, metastatic spread portendsthe worst prognosis and serves as the major branchpoint in guiding therapy [7]. At our institution, thosewith localized disease receive six cycles of neoadjuvant

therapy, definitive local control with surgery if feasible,then eight additional cycles of adjuvant chemotherapyfor consolidation. First-line drugs of proven efficacyinclude vincristine, actinomycin-D, cyclophospha-mide, doxorubicin, etoposide, and ifosfamide. Com-binations of similar chemotherapies are used in thosewith metastatic disease but experimental chemothera-pies are considered earlier and second-line regimenssuch as cyclophosphamide/topotecan, irinotecan/temozolomide, or high-dose ifosfamide are often usedimmediately after frontline therapy when bone marrowreserves allow for this. Aggressive use of chemotherapyis often associated with complete or major partialtreatment response, which occasionally enables cura-tive local control that would not be otherwise possible.While the prognoses for those with metastatic orrecurrence disease remain grim, a number of promisingtreatment options have transitioned from the labora-tory to the clinical within the last year. Insulin-likegrowth factor receptor 1 (IGF-1R) targeted agents (bothmonoclonal antibodies and small-molecule tyrosinekinase inhibitors) have perhaps received the mostattention recently, given preliminary phase I clinicaltrial results that suggest they are both well toleratedand markedly effective in a subset of those with chemo-refractory EWS. Phase II trials, selective for sarcomasubtypes including EWS, are underway to more fullyasses tumor response.

TreatmentDiagnosis and staging

• Since a number of pediatric malignancies (such as neuroblastoma,rhabdomyosarcoma, lymphoblastic lymphoma, desmoplastic smallround cell tumor (DSRCT), and poorly differentiated synovial sar-coma) are included in the differential diagnosis of small round celltumors, immunohistochemistry and molecular studies such asRT-PCR and fluorescent in situ hybridization (FISH) play a critical role inconfirming the appropriate diagnosis. Although the EWS-FLI1 trans-location is prototypical, rarer pairings of the TET family ofRNA-binding protein (TLS/FUS, EWS, TAFII68) with an ETS familytranscription factors (such as FLI1 or ERG) will not be detected usingbreak-apart EWS FISH. Thus, translocation-negative EWS have beenreported and should be treated as such, given an appropriate clinicalscenario [8]. Attempted molecular characterization of all Ewing familytumors is the evolving standard of clinical care in this disease, butmust be interpreted in the complete context of pathologic and diseasesetting [9–11]. A role for sequential RT-PCR monitoring of peripheralblood and/or bone marrow after therapy has been suggested to bothconfirm ‘‘complete’’ therapeutic response and to allow early detectionof minimal residual disease that is predictive of clinically detectable

Ewing’s Sarcoma Subbiah et al. 127

recurrence, but prospective trials of such approaches are needed [12].• Preliminary reports suggest the type 1 EWS-FLI1 translocation confers

a better prognosis than those with type II or other types of variants.However, until rigorously evaluated by a large clinical trial, such asEURO-EWING99, it is not presently used to stratify high- fromlow-risk patients in clinical trials [13–15]. In addition, the suggesteddifferences in outcome would be unlikely to modify the initial ther-apeutic approach since even type I disease is high risk.

• At this time, there is no well-accepted staging criterion for EWS. Pre-treatment planning should include plain X-rays of the involved bone,MRI of the spine (or bone marrow biopsy), chest CT, LDH, and eitherwhole-body bone scan or PET. Despite the fact that patients withmarrow-positive disease have been reported to be an adverse prog-nostic marker of survival, we do not routinely perform bone iliaccrest marrow biopsies to detect subclinical micrometastatic diseasesince both marrow-positive and -negative patients alike are treatedwith extensive systemic chemotherapy. FDG-PET/CT scans have oftenbeen especially helpful for determining early clinical response totherapy and for planning radiotherapy for surgically unresectablelocations. As described previously, the presence or absence of meta-static disease at diagnosis is the single most important criterionguiding initial treatment.

Localized disease• Conceptually, treatment for those with localized disease includes

three distinct phases: cytoreduction (to eradicate micrometastaticdisease and facilitate effective local control measures with wide neg-ative margins); definitive local control to eradicate all known disease(surgery when possible); and adjuvant chemotherapy to minimizetumor recurrence [16]. Chemotherapy response is monitored radio-graphically to evaluate clinical response and, in the setting of pro-gressive disease, patients receive either alternative chemotherapy orpreoperative radiation.

• Before the modern chemotherapy era 40 years ago, less than 10% ofthe EWS patients survived [17]. Local control relied extensively uponradiation therapy, rather than surgery, and most died soon afterdiagnosis with pulmonary metastases. In 1962, cyclophosphamidewas the first drug shown to improve local control of Ewing’s [18, 19].A decade later, other chemotherapies including vincristine, actino-mycin-D, daunomycin, and doxorubicin were also shown to beeffective in combination with radiotherapy [20–23]. In 1974, Rosenet al. [24] at Memorial Sloan-Kettering Cancer Center combined thesechemotherapies (vincristine, actinomycin-D, cyclophosphamide, anddoxorubicin (VAcCD)), signaling the advent of multimodality therapyusing chemotherapies that remain the backbone of contemporaryEWS treatment. At least eight multi-institutional collaborative trialsconducted through the mid-‘80s, both within (IESS I and II, ES-79,and POG 8346) and outside the United States (Germany’s CESS 81,UK’s ET-1, Italy’s REA-2, and French SFOP EW84), have confirmed theclinical benefit of a VAcCD-based regimens [25–27] (Fig. 1).

• Regimens that incorporate ifosfamide and/or etoposide with three ormore of the previous VAcCD-based chemotherapies have furtherimproved event-free survival for patients with localized, but notmetastatic, disease and therefore represent the current standard of carefor frontline therapy [28, 29]. Strategies designed to optimize their

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combined clinical effect have attempted to maximize the chemo-therapy dose per cycle, increase the total number of cycles provided, ordecrease the interval between cycles. The Children’s OncologyGroup’s (COG) AEWS-0031 trial, which compared alternating coursesof VDC (vincristine, doxorubicin, and cyclophosphamide) and IE(ifosfamide and etoposide) provided either in a ‘dose-dense’ fashionevery 2 weeks or every 3 weeks, is an example of this approach. Pre-liminary results (ASCO 2008) suggest that dose-dense therapy sig-nificantly improves survival in patients younger than 18 years old[30]. Why this benefit in dose-dense apparently failed to improve theoutcome of older patients is unknown. Since this study enrolled onlya limited number of adult EWS patients and was insufficiently pow-ered to detect a small clinical benefit (if it exists), further clinical trialinvestigation is warranted before a dose-dense strategy is applied tothe adult EWS population.

• At MD Anderson Cancer Center, treatment of localized EWS variesslightly depending upon patient age. Adults with EWS are treated withthe neoadjuvant combination of vincristine, doxorubicin, and ifosfa-mide (with mesna) provided every 3 weeks for six cycles whereaschildren typically receive alternating VDC and ifosfamide/etoposide(IE) as described above. Preoperative restaging is obtained and

UK

EuropeUSA

IESS-1 (73-78)

IESS-2(78-82)

INT-0091(88-92)

St.Judes ES-79-(78-86)ES-87(87-91)EW-92(92-96)

POG-CCG(95-98) MSKCC

T2-70-78P6-90-95,P6-91-01

SSG-ScandinaviaSSG IX(90-99)

SFOP-FranceEW-88(88-91)

ROI Bologona/ItalyREN-3(91-97)

UKCCSG/MRCET1(78-86)ET2(87-93)

EI-CESS-92(92-99)-UK+Germany

EURO-EWING-99Europe –(99-Current)

CESS(Germany)CESS-81(81-85)CESS-86(86-91)

COG-AEWS-0031(01-05)

Future?

Figure 1. Large multi-institutional collaborative trials in USA and Europe—past and current. USA: IESS,Intergroup Ewing’s Sarcoma Study; POG-CCG, Pediatric Oncology Group Children’s Cancer Group; INT009; COG,Children’s Oncology Group; MSKCC, Memorial Sloan Kettering Cancer Center, New York; St. Judes, St. JudesResearch Hopital, Tennessee, Memphis. Europe: Germany: CESS, Cooperative Ewing Sarcoma Study. UK: ET Ewing’stumor; UK + Germany: EI–CESS, European Intergroup Cooperative Ewing’s Sarcoma Study; Scandinavia: SSG,Scandinavian Sarcoma Group; EURO-E.W.I.N.G.99, EUROpean Ewing tumor Working Initiative of National GroupsEwing Tumor Studies 1999; France + Austria + Switzerland + members of the European Organization for Researchand Treatment of Cancer Soft Tissue and Bone Sarcoma Group + UK + Germany

Ewing’s Sarcoma Subbiah et al. 129

followed by surgery of the primary tumor unless negative margins orsubstantial morbidity would be predicted; definitive radiation isprovided otherwise. While patients convalesce from surgery over a3- to 4-week period before starting adjuvant therapy, our pathologistsassess the extent to which neoadjuvant therapy induced tumornecrosis (reported in percentage). Though all patients are universallytreated with eight or more additional cycles of chemotherapy (for atotal of 14), the type of chemotherapy chosen is personalized toaccount for each individual’s response to neoadjuvant treatment.Those with either no reduction in tumor size or suboptimaltumor necrosis within their surgical specimen (less than 98% basedon institutional experience) are treated with second-line regimenstypically reserved for those with metastatic spread (high dose ifosfa-mide, topoisomerase I inhibitor/alkylating agent combinations, etc.)[31]. This approach is similar to that taken in the ongoing EURO-EWING99 trial, which randomizes poor-chemotherapy-responders toreceive either seven additional cycles of VAcI or high-dose Melphalan-based chemotherapy with autologous stem cell rescue.

• Known to be radiation sensitive since the earliest clinical reports,localized EWS tumors had been treated throughout most of the 20thcentury primarily with radiation [32–34]. Today, both improvementsin surgical technique (that avoid amputation, preserve function, andachieve high local control) and a greater appreciation of the risksassociated with radiation (such as leg-length disparity and rare sec-ondary malignancies) have reduced the reliance upon radiation.Though there are no randomized controlled studies that directlycompared surgery to radiation for definitive local control, most largeclinical trials report local failure rates nearly three-fold higher inpatients treated with radiation alone (30% failure) compared tosurgery alone (10% or less) [35–38]. Selection bias for those withlarger, unresectable tumors may partially explain this difference, butour institutional practice echoes that of most other centers, favoringsurgery unless margin-negative resection is unachievable or morbid. Ifradiation is necessary, results from St. Jude Children’s ResearchHospital indicate that more than 40 Gy is associated with improvedlocal control. COG protocols currently use 55.8 Gy dose [39]. Tumordebulking prior to radiation has failed to improve local controlcompared to radiation alone and should be avoided. Though infre-quently used, proton therapy may allow for improved delivery ofradiation to the tumor in certain sites while limiting the exposureof adjacent normal tissues to scatter-related effects of conventionalradiation. Proton radiation has greatest advantage in axial locationssuch as skull base and sacrum.

• Older age (>14 years) has consistently been associated with a poorsurvival outcome from EWS [28, 40–44]. The explanation for thisremains unclear, as recent studies suggest no difference in metastasisat diagnosis (28%), tumor location, or histological response to neo-adjuvant therapy [45–47]. Two differences reported by Pieper et al.[48] were an increase in tumor size and a higher proportion ofextraskeletal origin among patients >40 years enrolled in eitherEICESS 92 or EURO-EWING 99. As those treated at referralcenters with significant experience in EWS management appear tohave better outcomes, improved survival among children compared to

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adults could also be related to an increased familiarity of pediatric-oncologists treating this disease as has been suggested by Paulussenet al. [49]. Most recently, the AEWS-0031 trial, alternating vincristine,doxorubicin, and cyclophosphamide with ifosfamide/etoposide every2 instead of every 3 weeks, suggests that older patients (>18) failed tobenefit. Until a clear biological explanation for this is reconciled, theoptimal regimen used to treat adult EWS patients with localized dis-ease remains to be determined in future clinical trials.

• Pathologic assessment of response to therapy involves evaluation oftreated tumor for degree of necrosis similar to what is done for oste-osarcoma. Although there is general agreement that a completeresponse (inability to detect viable tumor cells with extensive sam-pling) is associated with better outcome than residual gross disease inthe resection specimen, more work is needed to establish uniformcutoffs linking degree of necrosis to disease-specific survival [44].Radiographic correlates of tumor necrosis may also provide importantinformation regarding treatment efficacy [50].

Recurrent or metastatic disease• Whereas chemotherapy often enables patients with localized disease

to be cured, in those with metastatic spread its benefit is more oftenlimited to extending progression-free survival [51, 52]. Durableresponses remain elusive. Overall survival of patients with metastaticdisease at the time of diagnosis remains around 25% and those withsolitary pulmonary metastases fare only slightly better than thosewith either isolated osseous metastases or spread to bone and lung(5-year event-free survival of 29, 19, and 8%, respectively) [40].Patients with recurrent disease within the first two years fare evenworse with 5-year survival around 7% (compared to 30% forrecurrent disease ‡2 years) [53]. This suggests that treatment ofmetastatic disease requires a fresh approach distinct from that forlocal control. Described below are treatment options available topatients both on- and off-study.

Options using commercially available agents• Cyclophosphamide is of course well studied in EWS with proven

efficacy [18, 19, 54]. Its combination with topotecan, a derivative ofcamptothecin that inhibits topoisomerase I, has proved to be syner-gistic, with proven efficacy first in pediatric solid malignancies col-lectively [55] and later for EWS [56]. Our experience using thecyclophosphamide/topotecan regimen for second-line therapy dem-onstrates both effectiveness, as the majority derive clinical benefitdefine by CR or PR, and safety [57]. As part of a clinical trial, topo-tecan is currently being included in the COG study and is beingcontemplated for inclusion in upcoming EURO-EWING trials(Table 1). Similarly, the combination of temozolomide and irino-tecan has also proved to be effective for EWS [58, 59]. These resultshave been confirmed internationally and, at present, either of the twocombinations should be considered for use as second-line or salvagetherapy [57]. In our hands, this regimen can be delivered outpatientwith limited cytopenias and has gained a warm reception amongyoung adults since alopecia is avoided [60]. Of significance, neithertopoisomerase I inhibitor appears to be effective when used alone.

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• Gemcitabine and docetaxel have proven benefit for the treatment ofsoft tissue sarcomas [61]. The Sarcoma Alliance for Research throughCollaboration (SARC) is currently accruing pediatric and adultpatients for a Phase II study of gemcitabine and docetaxel in relapsedESFT. EWS patients have been reported to respond to this regimen;however, it appears to be a small minority.

Whole lung irradiation (WLI)• Although metastatic sites should not routinely be resected, the

exception is for isolated pulmonary metastasis, where surgery may becurative in patients whose primary tumor was well controlled. Fol-lowing resection of limited lung-only metastases, irradiation may beconsidered. Since the CESS-I trial results were reported, there has beencontroversy regarding the potential benefit of WLI. In that trial, therate of pulmonary relapse following pneumonectomy significantlydecreased from 34% (VAcC alone) to 20% with the inclusion of WLI.However, because the addition of doxorubicin to VAcC chemotherapyreduced pulmonary relapse to 10%, without WLI, one could not becertain that WLI improved survival in those who receive a ‘modern’chemotherapy regimen that includes doxorubicin [27]. More recently,retrospective analysis of the EICESS-92 trial suggests a nonsignificanttrend toward improved survival (P = 0.363). Among the pediatricpopulation treated at our institution, most will receive low-dose WLIin the appropriate clinical setting whereas this is generally avoided inour adult population. The impact WLI has on patients that receivetoday’s combination of effective chemotherapies will hopefully bedetermined in a randomized, prospective fashion in the EURO-EW-ING 99 trial.

Experimental therapies (generally available only as part of a clinical trial)• As the number of prognostic biomarkers of potential importance

grows, so has the interest in using them as potential therapeutic targets[62, 63] (Fig. 2). Described below are several drugs, techniques, and/or biological targets in evaluation by large collaborative groupsexperienced in EWS management.

Table 1. Currently available Large Group Collaborative trials

Cooperativegroupor group/phase

Country Eligible patient criteria Comments

COG-AEWS0331* USA Isolated pulmonary or pleural metastases

at the initial diagnosis of Ewing’s sarcoma

VDC + IE with/without topotecan

SARC 003/Phase II USA Recurrent ESFT Gemcitabine + docetaxel

EURO-EWINGS 99/

Phase III

Europe 1. Newly diagnosed-nonmetastatic 1. VAI vs VAC; VAI vs. HDT

2. ESFT with lung mets 2. VAI + pulmonary radiotherapy vs HDT

SARC-011/Phase II USA Recurrent or refractory Ewing’s sarcoma R1507, a recombinant human monoclonal

antibody to the IGF1-R

*R2 Randomization of EURO-EWINGS 99.

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BMT

• The vast majority of clinical evidence suggests that bone marrow (orperipheral blood stem cell) transplants fail to improve survival whencompared to historical controls [41, 64–68]. That overall survival

Figure 2. Targets for Ewing’s current options and possible future therapies. Abbreviations: IGF1R, insulin-likegrowth factor; GRB2, growth receptor binding protein 2; SOS, exchange factor Son of sevenless; MAPK/ERK ½,mitogen-activated serine/threonine protein kinase (MAPK) or extracellular signal-regulated kinase (Erk); P1P2,phosphatidyl inositol 4-5 bisphosphate; P1P3, phosphatidyl inositol 3 kinase; PTEN, phosphatase and tensinhomolog; mTOR, mammalian target of rapamycin; S6K, protein S6 kinase; 4EB1, eukaryotic initiation factor 4Ebinding protein-1; PDGFR, platelet derived growth factor receptor; EGFR, epidermal growth factor receptor; HER2/NEU, human epidermal growth factor receptor 2; VEGFR, vascular endothelial growth factor receptor; HDAC,histone deacetylases; TKI, tyrosine kinase Inhibitors. IGF1-R system: IGF1R, a tyrosine kinase traverses the plasmamembrane and is composed of 2 ab chains. The IGF ligands found in circulation binds with varying affinities tothe receptor. Activation of IGF-1R leads to phosphorylation of adaptor proteins of IRS or SHC family. Activation ofIRS and SHC leads to ERK1/2 of MAPK cascade via GRB2 fi SOS fi RAS fi RAF fi MAPK pathway. IRSprotein approximates to P13K leading to P1P3. This is followed by AKT activation, then PDK1. This leads todownstream activation of mTOR (mTOR, mlST8 and raptor) activation. Activation of mTOR phosphorylates S6K1and 4E-BP1 (top-dependant and cap-dependant translation). As indicated they all are implicated in proliferation,migration, differentiation, and autophagy of the Tumor. EWS-FL1 fusion protein resulting from t(22:11)translocation serving as aberrant transcription factors. Currently available cytotoxic chemotherapeutic options(standard and commercially available). Other agents: pre-clinical or tested in other soft tissue sarcomas. TKI as apotential treatment option. As a family they make up the maximum number of signaling pathways which includeIGF1-R (expanded in A) and others like PDGFR, c-KIT, VEGFR, HER2/neu which may have potential

Ewing’s Sarcoma Subbiah et al. 133

remains unchanged despite a significant risk of death approaching8% from treatment-related complications (treatment-related leuke-mia and myelodysplastic syndromes (t-AML/MDS), graft-vs-hostdisease, and infection) indicates that a small subset who avoid acutetoxicity achieve long-term survival [69]. Too few patients have beentreated using allogeneic stem cell transplant to ascertain its clinicaleffect, however, a recent case report interestingly noted potentialgraft-vs-tumor effect in one patient [70]. Pending results from theBMT arm of EURO-EWING 99, neither autologous nor allogeneictransplant should be offered to patients outside of a clinical trialsetting.

VEGF inhibition

• Vasculogenesis in addition to angiogenesis plays an important role inEWS in vivo [71]. Given high levels of VEGF expression in vitro and amurine model that suggest a role for angiogenesis in EWS tumor for-mation, the combination of bevacizumab (Avastin�) with vincristine,cyclophosphamide and topotecan is being evaluated in the COG-AEWS-0521 trial in patients with recurrent Ewing’s sarcoma. Otheragents like sunitinib and semaxanib may also have potential[57, 71, 72].

Ecteinascidin 743 (ET-743; Yondelis�, Trabectedin)

• Trabectedin is a murine derivative from the Ecteinascidia turbinate(sea squirt) that, unlike other alkylating agents, binds the N2 positionof guanine in the DNA minor groove [73–75]. It has proven efficacy asa third-line agent for subtypes of soft tissue sarcoma, but its effectremains to be determined for EWS. This agent is approved in Europefor sarcomas.

EWS/FL1

• In vitro downregulation of the EWS:FLI1 translocation via antisenseoligonucleotides, dominant-negative transcripts, and RNAi has beenshown to limit malignant transformation and reduce cell growth[76–79]. Translation of these basic science findings to the clinicalsetting remains challenging, limited in part by the inability for theseagents to enter the cell as required to exert their respective effects.Another strategy is to impair the down-stream effects of EWS-FLI1transcription. It was reported recently that EWS cells treated withcytarabine in vitro induced a genetic signature indicative of morequiescent EWS/FLI-‘‘off’’ state [80]. This was reinforced by xenograftand cell line studies. The COG-AEWS-0621 study of cytarabine inpatients with EWS, unfortunately, demonstrated minimal activity andsignificant hematologic toxicity [81].

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Insulin-like growth factor-1 receptor (IGF-1R)

• IGF1-R plays an important role in transformation, apoptosis protec-tion, invasion and metastasis, and resistance. Ubiquitous in EWS, IGF-1R is a tyrosine kinase receptor with approximately 50% homology tothe insulin receptor [82]. Preclinically, activation of this receptor hasbeen found to be essential for EWS-FLI-1 induced malignant trans-formation of murine fibroblasts [83]. Influenced by EWS-FLI-1, EWSappears to exploit an activated IGF-1R pathway as a key step inmalignant transformation. Upon binding of the EWS/FLI-1 fusionprotein to the insulin-like growth factor binding protein (IGF-BP3)promotor, IGF-BP-3 transcriptional activity is reduced, free IGF-BP-3decreases, and more IGF-I ligand is available for ligand-induced acti-vation of the ubiquitous IGF1R [84, 85]. This positive feedback loopdriving neoplastic cell growth and metastasis is reinforced by down-stream activation of the mitogen-activation protein kinase (MAPK)and phosphatidylinositol-3-kinase (PI3-K)/Akt pathways that shift theregulatory balance in favor of cell survival rather than apoptosis [86].Given the weight of evidence suggesting an important role for IGF-1Rinhibition for EWS and other cancer types, clinical development hasbeen pursued. The Pediatric Preclinical Testing Program showed initialactivity of IGF-1R-targeted monoclonal antibodies (mAb) in a murinexenograft model of human EWS. In a phase I trial conducted by ourinstitution’s Experimental Therapeutics Program, four of nine patientsappeared to derive clinical benefit from mAb-based single-agenttherapy without significant toxicity. SARC and other large collabora-tive group have begun phase II trials limited to sarcoma patients,including EWS, and the results are eagerly awaited (Fig. 3). Althoughnot yet in clinical trials, Manara et al. [87] have reported uponNVP-AEW541, a small-molecule IGF-1R antagonist with preclinicalefficacy against Ewing’s cell xenografts in murine models.

mTOR

• Given that mTOR serves as a potential bypass pathway for IGF-1Rtargeting, its inhibition in combination with IGF-1R suppression mayprove synergistic. Similarly, combined inhibition of IGF-1R and

Figure 3. Response of a patient to IGF-1R targeted therapy—before and after 7 weeks of treatment

Ewing’s Sarcoma Subbiah et al. 135

mTOR may avoid the counterproductive rapamycin-induced upregu-lation of Akt that occurs within 6 h of treatment. Phase I clinical trialsare currently open to investigate this potential synergy.

Preclinical• Preclinical models have demonstrated value in designing clinical

studies investigating epigenetic treatment approaches. 5-Aza-2¢-deox-ycytidine and MS-275 may be possible candidates in patients withadvanced Ewing’s sarcoma [88].

• Tubulin binding vascular disrupting agents (VDAs) like OXi4503/CA1P slows subcutaneous ESFT growth. In combination with con-ventional cytotoxic agents or hypoxia-activated prodrugs, this mayprovide a novel therapeutic strategy to treat ESFT [89].

• Though EWS-FLI-1, or an alternative fusion variant, appears to benecessary for transformation and growth, it is not sufficient without acomplex interplay of activated molecules such as IGF-1R, mTOR,MAPK, PI3K/Akt, EGFR, VEGF, and the like [90]. Highlighting this,many of these molecules and others (or their associated pathways)were found to be dysregulated, as assessed by gene microarray, inpatients whose tumors responded poorly to neoadjuvant therapyprovided as per the EURO-EWING99 protocol [91]. Other potentialtargets include the Wnt signaling pathway [92], the Hedgehog sig-naling pathway [93, 94], and the p53 pathway. The relationship ofthose pathways with the downstream effects of the fusion protein aretopics of active research.

Conclusion• Multimodality care that incorporates progress in surgical technique,

radiation, and poly-chemotherapy has dramatically improved thesurvival of EWS patients that present with localized disease. This is nottrue, unfortunately, for those with metastatic or recurrent disease;5-year survival has remained fixed at 25–29%. Poor prognostic factors(such as older patient age, high tumor volume, pelvic location, andinadequate response to chemotherapy) remain as true today as whenthey were first described. Recognizing the need for a paradigm shiftcaring of poor-risk patients, most collaborative group trials nowstratify patients to promote the use of novel, investigational therapiesin high-risk subsets. Some of the most promising drugs have beendescribed, yet they remain rarely used. As the molecular etiologiesresponsible for poor prognosis become better understood—throughgreater reliance upon patient specimens and improved integration ofpharmacodynamic endpoints into clinical trials—we will increasinglybe able to circumvent those mechanisms using less toxic and moretargeted personalized biological therapies. Already, this process hasbegun in earnest, with clinical trials designed to affect specific path-ways or interfere with known mechanisms of resistance. The study ofIGF-1R inhibitors and other targeted therapies represents just thefirst step in the journey to ‘make cancer history’.

Acknowledgments We thank Kim-Anh Vu for the graphicdesign. Grant support: UT MD Anderson Cancer Center Intra-mural funding (J.A.L.), UT MD Anderson Physician Scientistprogram (A.J.L.) and Jeremy Rosen Memorial fund (P.A.).

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